Ammonia is an important chemical in industry and agriculture. It is used in the manufacture of many polymers and textiles, as well as being the essential foundation of nitrogen fertilizers.
Ammonia found in air or water may originate from the decomposition of urea, proteins, and other nitrogenous organic substances, or from the accidental escape of ammonia during its use in industry or agriculture. Ammonia in air is toxic to humans and animals at concentrations of 25 to 500 parts per million, depending on the acceptable exposure time. At any concentration, ammonia in air combines with acidic components, such as sulphur dioxide, to form particulate matter less than 2.5 um diameter (PM2.5), which is a particularly noxious pollutant that can penetrate deep inside the human respiratory tract. In addition, airborne ammonia causes corrosion of metal structures and is considered to be a major contributor to odour problems.
Ammonia is highly soluble in water, where it can cause fish mortality at high concentrations and contribute to eutrophication and a depletion of oxygen by stimulating the growth of algal populations.
Ammonia may be removed from air by several methods. First, and most inexpensively, ammonia-laden air is diluted with air of low ammonia concentrations so that acceptable levels are achieved. However, this “dilution” approach distributes ammonia over a wider area and thus contributes to the formation of PM2.5. In confined livestock operations, where toxic levels of ammonia build up as a result of animal urine deposition, inside air is expelled and outside air is brought in as “make-up air”. However, under cold climate conditions, the removal of ammonia-laden air requires heating of replacement air to keep even temperatures inside the barn.
Another option is to remove ammonia from air by bubbling it through water, thereby trapping the ammonia as aqueous ammonia and ammonium ion (NH4+). However, as ammonium levels increase, the pH of the water increases and ammonia is released into the air again. Furthermore, dilute ammoniated water is not valuable and must be disposed of as well. A third option, and perhaps the most common of all, is to bubble ammonia-laden air through mineral acids, such as sulphuric or hydrochloric or nitric acid. The ammonia is converted to the equivalent salt (ammonium sulphate, ammonium chloride or ammonium nitrate). The disadvantages of the third option are: (a) considerable back pressure develops as a result of bubbling air through liquids and (b) the salts that are formed are mixed with the liquid acid and are difficult to separate, thereby limiting the usefulness of the by-products.
Another option is to reduce ammonia to nitrogen gas (N2) by electrochemical treatment, however, this method suffers from high operating costs and the requirement for complex processing equipment.
If ammonia must be removed from water, such as from wastewater that will be reintroduced to natural water bodies, the ammonia is stripped from the water into air, where it becomes an air-removal problem again. Therefore, all of the technologies discussed above for removing ammonia from air are equally applicable to treating ammonia in water.
Therefore, there is a need in the art for a activated carbon matrix that removes ammonia from air, which may mitigate some or all of the difficulties found in the prior art.